1. Field of the Invention
The present invention relates to a shadow mask for a cathode ray tube, and in particular, to a shadow mask for a cathode ray tube that defines a range of the minimum radius of curvature to improve properties in shock and howling simultaneously.
2. Description of the Related Art
Generally, a cathode ray tube is an electronic tube where electron beams emitted from an electron gun are deflected due to a magnetic deflection field, pass through a color selection shadow mask, and then strike and excite green, blue, and red phosphors on a phosphor film within a panel, thereby displaying desired images.
The shadow mask has a color selection function of selecting the emitted electron beams and landing them on the phosphor film.
The shape of the shadow mask is determined according to size and shape of a panel, that is, a front plane glass of the cathode ray tube. The shadow mask is formed with a radius of curvature of about R=2000 mm (millimeters) generally.
Recently, cathode ray tubes have become larger, and the front surface of the panel has been flattened. Accordingly, the shape of the shadow mask has changed to correspond to these tendencies of the cathode ray tube.
However, when the shadow mask has a large size and a large radius of curvature, the structural strength of the shadow mask becomes poor, and this may induce many problems.
That is, when the radius of curvature of the shadow mask is 1.6R or more, the shadow mask cannot maintain its own shape due to shocks from the outside. Deformation of the shadow mask deteriorates the quality of the cathode ray tube.
In addition, when the shadow mask has a large size and a large radius of curvature, it has poor properties in howling. That is, when the cathode ray tube with the shadow mask is used as a television, the shadow mask trembles due to the sound of the television. In this case, the shadow mask becomes fragile by the howling phenomenon due to the weakness of the structural strength.
When the outer surface of the panel is formed with a flat shape and has a large inner radius of curvature, the radius of curvature of the shadow mask also increases. Accordingly, the shadow mask becomes flat.
When the curved plane of the shadow mask becomes partially flat, deformations occur in the flat portion of the curved plane due to the shock load from the outside.
As the shock load is applied continually, the deformations are transferred to the edge portions of the shadow mask. Accordingly, plastic deformations occur in the shadow mask, and the electron beams emitted from the electron gun are distorted during passing through the shadow mask. Accordingly, the electrons cannot cause correct emission of the phosphors, and trembling of the images and deterioration of color purity occurs.